Spring data JPA中使用Specifications动态构建查询

有时我们在查询某个实体的时候，给定的条件是不固定的，这是我们就需要动态 构建相应的查询语句，在JPA2.0中我们可以通过Criteria接口查询，JPA criteria查询.相比JPQL,其优势是类型安全,更加的面向对象.而在Spring data JPA中相应的接口是JpaSpecificationExecutor，这个接口基本是围绕着Specification接口来定义的。 Specification接口中只定义了如下一个方法：

Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder cb);

1	Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder cb);

我们只需要重写这个方法即可，相关知识请自行查阅JPA Criteria查询 

过滤条件

1：过滤条件会被应用到SQL语句的FROM子句中。在criteria 查询中，查询条件通过Predicate或Expression实例应用到CriteriaQuery对象上。

2：这些条件使用 CriteriaQuery .where 方法应用到CriteriaQuery 对象上

3：CriteriaBuilder也作为Predicate实例的工厂，通过调用CriteriaBuilder 的条件方法（ equal，notEqual， gt， ge，lt， le，between，like等）创建Predicate对象。

4：复合的Predicate 语句可以使用CriteriaBuilder的and, or andnot 方法构建。

相关代码如下，在这个例子中我们定义了2个类Articel和User类

Article:

@Entity
@Table(name = "t_article")
public class Article implements Serializable{
private static final long serialVersionUID = 6112067846581696118L;
@Id
@GeneratedValue
private Integer aid;
private String title;
@Temporal(TemporalType.TIMESTAMP)
private Date postTime;
@Temporal(TemporalType.TIMESTAMP)
private Date lastEditTime;
private String ip;
private String tag;
private boolean forbidComment;//禁止评论
@ManyToOne
@JoinColumn(name = "uid")
private User user;

private boolean recommend;//是否是推荐
@Temporal(TemporalType.TIMESTAMP)
private Date recommendTime;//推荐时间

//setter/getter略
}

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@Entity @Table(name = "t_article") public class Article implements Serializable{     private static final long serialVersionUID = 6112067846581696118L;     @Id     @GeneratedValue     private Integer aid;     private String title;     @Temporal(TemporalType.TIMESTAMP)     private Date postTime;     @Temporal(TemporalType.TIMESTAMP)     private Date lastEditTime;     private String ip;     private String tag;     private boolean forbidComment;//禁止评论     @ManyToOne     @JoinColumn(name = "uid")     private User user;       private boolean recommend;//是否是推荐     @Temporal(TemporalType.TIMESTAMP)     private Date recommendTime;//推荐时间       //setter/getter略 }

User:

@Entity
@Table(name = "t_user")
public class User implements Serializable {

private static final long serialVersionUID = 3703405133265901053L;
@Id
@GeneratedValue
private Integer uid;
private String nickname;
private String password;
//setter/getter略
}

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@Entity @Table(name = "t_user") public class User implements Serializable {       private static final long serialVersionUID = 3703405133265901053L;     @Id     @GeneratedValue     private Integer uid;     private String nickname;     private String password;      //setter/getter略 }

其中user和article是一对多的关系，是单向的

封装的查询实体SearchArticle

public class SearchArticle implements Serializable{
private static final long serialVersionUID = -1082122462716689486L;
private int page = 1;
private int limit;
@DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")
private Date postTimeStart;
@DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")
private Date postTimeEnd;
@DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")
private Date recTimeStart;
@DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")
private Date recTimeEnd;

private String nickname;

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public class SearchArticle implements Serializable{     private static final long serialVersionUID = -1082122462716689486L;     private int page = 1;     private int limit;     @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")     private Date postTimeStart;     @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")     private Date postTimeEnd;     @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")     private Date recTimeStart;     @DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")     private Date recTimeEnd;       private String nickname;

下面是查询方法

@Autowired
private ArticleRepository articleRepository;

@Override
public QueryResult<ArticleModel> findArticle(SearchArticle
searchArticle) {
Sort sort = new Sort(Sort.Direction.DESC,"postTime");
Specification<Article> specification =
getWhereClause(searchArticle);
Page<Article> all =
articleRepository.findAll(specification, new
PageRequest(searchArticle.getPage() - 1,
searchArticle.getLimit(),sort));
QueryResult<ArticleModel> result = new
QueryResult<>();
List<ArticleModel> list = new
ArrayList<>(searchArticle.getLimit());
for (Article article:all.getContent()){
ArticleModel model = new
ArticleModel(article.getAid(),article.getTitle(),article.getPostTime(),article.isRecommend(),

article.getRecommendTime(),article.getIp(),article.getUser().getUid(),article.getUser().getNickname());

list.add(model);
}
result.setRows(list);
result.setTotal(all.getTotalElements());
return result;
}

/**
* 动态生成where语句
* @param searchArticle
* @return
*/
private Specification<Article> getWhereClause(final
SearchArticle searchArticle){
return new Specification<Article>() {
@Override
public Predicate toPredicate(Root<Article> root,
CriteriaQuery<?> query, CriteriaBuilder cb) {
List<Predicate> predicate = new
ArrayList<>();
if(searchArticle.getPostTimeStart()!=null){

predicate.add(cb.greaterThanOrEqualTo(root.get("postTime").as(Date.class),
searchArticle.getPostTimeStart()));
}
if(searchArticle.getPostTimeEnd()!=null){

predicate.add(cb.lessThanOrEqualTo(root.get("postTime").as(Date.class),
searchArticle.getPostTimeEnd()));
}
if(searchArticle.getRecTimeStart()!=null){

predicate.add(cb.greaterThanOrEqualTo(root.get("recommendTime").as(Date.class),
searchArticle.getRecTimeStart()));
}
if (searchArticle.getRecTimeEnd()!=null){

predicate.add(cb.lessThanOrEqualTo(root.get("recommendTime").as(Date.class),
searchArticle.getRecTimeEnd()));
}
if
(StringUtils.isNotBlank(searchArticle.getNickname())){
//两张表关联查询
Join<Article,User> userJoin =
root.join(root.getModel().getSingularAttribute("user",User.class),JoinType.LEFT);

predicate.add(cb.like(userJoin.get("nickname").as(String.class), "%" +
searchArticle.getNickname() + "%"));
}
Predicate[] pre = new Predicate[predicate.size()];
return
query.where(predicate.toArray(pre)).getRestriction();
}
};
}

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@Autowired     private ArticleRepository articleRepository;      @Override     public QueryResult<ArticleModel> findArticle(SearchArticle searchArticle) {         Sort sort = new Sort(Sort.Direction.DESC,"postTime");         Specification<Article> specification = getWhereClause(searchArticle);         Page<Article> all = articleRepository.findAll(specification, new PageRequest(searchArticle.getPage() - 1, searchArticle.getLimit(),sort));         QueryResult<ArticleModel> result = new QueryResult<>();         List<ArticleModel> list = new ArrayList<>(searchArticle.getLimit());         for (Article article:all.getContent()){             ArticleModel model = new ArticleModel(article.getAid(),article.getTitle(),article.getPostTime(),article.isRecommend(),                     article.getRecommendTime(),article.getIp(),article.getUser().getUid(),article.getUser().getNickname());             list.add(model);         }         result.setRows(list);         result.setTotal(all.getTotalElements());         return result;     }       /**      * 动态生成where语句      * @param searchArticle      * @return      */     private Specification<Article> getWhereClause(final SearchArticle searchArticle){         return new Specification<Article>() {             @Override             public Predicate toPredicate(Root<Article> root, CriteriaQuery<?> query, CriteriaBuilder cb) {                 List<Predicate> predicate = new ArrayList<>();                 if(searchArticle.getPostTimeStart()!=null){                     predicate.add(cb.greaterThanOrEqualTo(root.get("postTime").as(Date.class), searchArticle.getPostTimeStart()));                 }                 if(searchArticle.getPostTimeEnd()!=null){                     predicate.add(cb.lessThanOrEqualTo(root.get("postTime").as(Date.class), searchArticle.getPostTimeEnd()));                 }                 if(searchArticle.getRecTimeStart()!=null){                     predicate.add(cb.greaterThanOrEqualTo(root.get("recommendTime").as(Date.class), searchArticle.getRecTimeStart()));                 }                 if (searchArticle.getRecTimeEnd()!=null){                     predicate.add(cb.lessThanOrEqualTo(root.get("recommendTime").as(Date.class), searchArticle.getRecTimeEnd()));                 }                 if (StringUtils.isNotBlank(searchArticle.getNickname())){                     //两张表关联查询                     Join<Article,User> userJoin = root.join(root.getModel().getSingularAttribute("user",User.class),JoinType.LEFT);                     predicate.add(cb.like(userJoin.get("nickname").as(String.class), "%" + searchArticle.getNickname() + "%"));                 }                 Predicate[] pre = new Predicate[predicate.size()];                 return query.where(predicate.toArray(pre)).getRestriction();             }         };     }

其中的 ArticleRepository接口如下，spring data jpa不需要你自己实现dao的接口

public interface ArticleRepository extends JpaRepository<Article,Integer>,JpaSpecificationExecutor<Article> {}

1	public interface ArticleRepository extends JpaRepository<Article,Integer>,JpaSpecificationExecutor<Article> {}

通过以上的步骤，我们就能构建相应的查询sql了，使用这个接口要对JPA2.0中Criteria查询有一定的了解